Wednesday, 22 January 2014

Creative Convolution Part 1 - Resonate

Convolution reverb is a great thing. Its
usual use - being able to capture and re-create spatial acoustics, is useful for a range of tasks such as fitting dialogue in a scene, or just creating
a sense of space. But it's worth taking a moment to think about what is
happening during this process. One sound file is effectively being filtered
through another, with the convolution reverb filtering the frequency content of
each sample through all the samples present in the IR (a simple explanation,
but adequate here). The impulse response files themselves effectively hold a snapshot of the
acoustic data of a space, or at least from a point in the space. This data describes how the room responds acoustically to an impulse or short burst of broadband noise. So essentially, you could think of
this in a different way, about sound files as containers of information -
acoustic information. But this
data is made up (like any sound file) of frequency content over time, so the
convolution reverb process is potentially useful for much more than just recreating
the acoustic space of a room; it is effectively a kind of filter, and that is the main subject here - an
exploration of that idea. I once heard a really useful definition of
timbre: “spectral footprint over time”. From a sound design perspective getting
the correct timbre for a sound is important as it connects the sound to its source. Interestingly, we naturally identify sounds back to their source (or object which created the sound) rather than by their acoustic properties. This explains why timbre is so important - it immediately describes the source, ie
hollow or metallic, and gives the listener an impression of what created the sound.If you found your way here, I expect you
might be familiar with this SoundWorks video for the making of Inception. I really love the bit at 3:20 where Richard King is describing the subwoofer
recordings they made in the warehouse; there is something fascinating about how
powerful and complex the natural resonances of the space are.

I've long had an interest in physical
modelling as a technique for designing sounds, so when I saw that video I started wondering what it would take to achieve the same results artificially. Would it be possible to model the space and materials of a location like that and produce some useful sounds? I think that understanding some of
the principles of physical modelling are useful not just for creating sounds to use, but also to help
explain how and why sound works in the way it does. I've done a few experiments
in Max using filterbanks and basic waveguides to try and simulate real-world
physical resonances with varying degrees of success, but experimenting
with convolution about a year ago, I discovered some interesting techniques which
are related…it started with a set of recordings like
these:These are impacts on various metal objects
recorded with a contact transducer. If you’ve ever used one of these, you will
know that one of the great things about recordings made in this way, is that they are completely dry, this is because the transducer only picks up the vibrations traveling
through the object itself. It means that you can go anywhere to record these
sounds, even next to busy roads where a conventional microphone recording would
be useless because of noise from the road. So I recorded a whole library
of these, experimenting with different objects and different methods of
striking them.It was while doing this that I had the
realisation – this process is exactly the same as taking impulse responses of rooms, I
was just collecting acoustic data. But when taking an IR of
a room, you are collecting data about how the room behaves acoustically, and
these recordings contain data about the resonance properties of the
material. The broadband noise used in recording an IR in a room, such as a balloon
burst, is comparable to the impulse created when striking an object. They are both a burst of broadband
noise followed by their effect on something – in the case of the room it is the
reverberant characteristics, with a material it is the resonant properties.Here’s an example of these sort of sounds
used as IRs in a convolution reverb, you will hear a dry vocal sample, then the
sound of the impact recorded with the contact transducer, then the vocal sample
through the convolution reverb with the impact loaded as an IR. You can hear
how the original sound is filtered through the resonance properties of the
material:It’s interesting to note how sounds with a
long decay still create a sound with a reverb-like quality to it, but sounds
with less decay create more of a filtering effect. Around this time two other things caught
my attention. Firstly, Alex Harker and Pierre Alexandre
Tremblay, both from Huddersfield University, released the HISS Tools - a
collection of Max objects designed for pretty much any convolution operation you can
think of (and a few more besides!). If you’ve used the Max for Live convolution
reverb before, they are at the heart of it. For sound designers these are an amazing addition to
Max, as they allow anyone to integrate convolution reverb
into any patch quickly and easily. Huge thanks to them for making these
objects publicly available.With this in mind I started sketching down some ideas for a
Max patch that would take advantage of these. It began as a kind of configurable resonant space, partly inspired by techniques used for mixing sounds
together in game audio, and partly from the experiments I’ve been describing.

The second thing that caught my attention
at that time, was this post at Designing Sound by Douglas Murray, focusing on his use of
convolution reverb to create infinite airfill using
white noise as a sound source. Up until this time I had been using a range of
sounds to ‘excite’ the IRs, but this was another direction, and really made so
much sense for creating ambient, atmospheric sounds. It’s a great technique,
and as an extension you can increase the resonance by
stacking up multiple instances of convolution reverb loaded with the same sound
as an IR. Here’s an example similar to before but with one, two, three and four
instances of the same reverb running in series.

When using white noise as a source, with
one instance of reverb you will always hear the noise coming through to some
degree, but with two or more instances the sound becomes progressively more
filtered and the dominant harmonics of the IR become accentuated. Be careful if you want to try this inside
a regular DAW – there will need to be some heavy gain reduction somewhere in
your signal chain, otherwise extreme clipping will result!Sounds of this kind are really useful for
creating evocative ambiances or adding some extra resonance to metal hits and scrapes.
I like the idea of having a palette of sounds like these, based just on
texture, using these in layers the same way a painter would with oils on
a canvas.So how about expanding this idea? There is certainly scope with this. I spent a bit of time designing
sounds for this purpose, and that is definitely worth pursuing, but I’m not
going to go too far into them here. Instead, I want to talk about another
technique for generating interesting sounds for use as IR’s. Whilst designing specific
sounds, I started experimenting with using music tracks as a source for IR's. I’d
snip out small sections of music with interesting harmonics then load them as IR's into
multiple reverbs and play noise or filtered noise through them. The resulting
sound is like a constant smear of all the frequencies present in the music, sounding similar to the results you can achieve with granular synthesis but with a richer sound. Bored of slicing music up manually I made
a small utility patch to automate the process. It takes a sound file and chops
it into smaller slices. The patch is fairly crude, but it works fine for the purposes of this article. To work flawlessly
it really needs to be a phasor-synchronised system, (feel free to improve it if
you like, but send me a better version if you do!). It’s reasonably
straightforward to use, just follow the instructions.

So that's a bit about the history of where the idea for this device originated. It actually references a whole bunch of work shared by other people, and tries to bring those ideas together and create something new. For me, this is all about tool building. Taking a process and re-thinking how it could work, combining existing technology in new ways to create new possibilities. It takes this process which in a DAW is very clunky and frustrating and reimagines the process. Everything here would be achievable with separate effects within a DAW, but in reality what you can achieve here in minutes would take hours of setting up and tweaking.

Here is the result, it is a device
which explores resonance, filtering and spatial positioning.

There are three sections to the patch, The sound source, the nodefield and the effects section. The sound source creates the sound used to feed the IR section of
the patch. There are currently three options here:

Loop Player - A vari-speed looping sound player with pitch and
amplitude envelope capabilities.

The middle section or what I've called the node field is the unique part of
the device. Here, there are eight FX lanes, each contains 2 IR reverb objects in
series. This is the signal flow inside each:

The output volume for each effects lane, or node, can
be linked to the node weighting (ie, how far into the node area the crosshairs
are). This is a linear value form 0-100% volume. Panning can be linked to the
position of each node across the X axis of the node field. If this is turned
off, the user can adjust the input volume of each by using the multislider at
the top of each fx chain. Pan position can also be linked to the position of
each node across the X axis of the nodefield. This generates
a stereo field across the X axis of the node field, so sounds can swept across
the resonators. There is a central system which distributes audio files to the
convolution reverb objects; this allows you to put all the
sound files you want to use as IR’s in a folder, point the patch to that folder
and then quickly choose between them from a menu system. A pair of LFO's are linked to the position of the cross hairs in the node field, these can be used to sweep across the nodefield, providing a spatial approach to mixing. There is also an envelope control labelled 'input gain scaling' which defines the shape of the gain slope, so you can have linear, exponential or any other gain curve, or even more complex, experimental patterns.The effects section below comprises of the following:

IR Reverb - Very basic convolution reverb. Comes pre-loaded with some IR's from the OpenAIR library

All the effects are combined using a matrix, so you can route audio through them in any combination, in parallel or in series. There is no feedback protection, so be careful there.I expect you're asking what does it sound like?Well I've been using it in a particular way, and have had that in mind through the development phase. But really it is just a combination of playback devices and effects, so use it however you see fit. Having said that, here are some examples, these are straight out of the app using the built in effects - no fancy external plugins.First up, a selection of static drones created with the white noise source. Note how the frequency fluctuations of the white noise add subtle but continuous variation to the drones: These are some metallic resonances created by using the contact mic recordings above as IR'sHere is an evolving drone which also uses white noise as a source but sweeps over the IR's using the LFO:This is a granular example. It takes a recording of a music box and plays it backwards with some position variation, it then filters this through some snippets of a female choir used as IR'sHere is some more radical granulation - frozen grain sweeps with some extra harmonic richness from the IR section.These sequences use white noise as a sound source. The noise has a rhythmic amplitude envelope and filter sweep applied to create an almost steam-like mechanical sound.

This application is fairly complex and dependent on external objects, so it seems best to distribute this as an application. However, the patch itself is licensed under Creative Commons:

Attribution-NonCommercial
CC BY-NC
This license lets others remix, tweak, and build upon your
work non-commercially, and although their new works must also
acknowledge you and be non-commercial, they don’t have to license their
derivative works on the same terms.

Here is a download link to the program. Currently this is Mac only, a windows version to come, I just need to sort out a few issues with that version.Resonate 1.0It comes loaded with a selection of the metal impacts, hence the download size, and should start making sounds as soon as you run the program. This is (currently) untested on any machine other than my own, so there may be some bugs - please report them in the comments section. I'm happy to share the patch with anyone interested, under the license you can alter it but not sell it. You are free of course, to create sounds with the program and use these however you like: commercial or non-commercial.

If you want to explore the patches themselves, you can find them here:

14 comments:

this is very interesting, i've been doing something similar assigning these impulse responses to specific speakers, thus getting spatial movement through convolution. Hiss tools are great, i just wish one could index the buffer, to be able to change responses on the fly....

I think the device is really quite amazing, sadly when I gave it a shot on my own "13 macbook with the same i5 (I assume) I also ran into trouble with it.It made my entire machine really bog down and the audio breaks up a lot.

Hi Mark, my name is Alan. I came across your work via the Max website. I am greatly impressed with your work - in particular being the 'Resonate'. I have no knowledge of synthesis, or sound design, and I was wondering could you give me some advice about how one would educate themselves on such topics, within the Max environment. I am not looking to re-invent the wheel of sound design - I am just looking to build small devices that I can make sound with. I am particularly interested in the field of minimalist composition, with Eliane Radigue being a prime example - your drones from the 'Resonate' were the exact tones I am in love with. A friend of mine recommended the Nord Modular, as it has modules pre-built, but I was wondering what your opinion on this is given your comment regarding your preference for Max over the DAW environment - I'm aware the Nord is not a DAW environment, but I would be interested to hear your opinion on whether or not Max is the ideal environment for an individual wanting to learn synthesis. I was considering purchasing the books by Maurizio Giri, and then following it up with the book by V.J. Manzo, along with going through the tutorials. Thank you for taking the time to read, and I hope you are well.

Hi Alan, pleased you are finding it interesting. As for the choice of tools for you to use, I think it is important to find a process which appeals to you and enables your creativity. It could be Max, the Nord or just a DAW and a portable recorder. There are no hard and fast rules as to which are 'better'. I still use a DAW all the time for other tasks. Having said that, Max is a great environment to learn about synthesis and the Giri book is excellent. I'd give a few things a try before taking the plunge - Max has a trial and I think you can download the Nord modular software from their site to try that out.

Hello Mark , Resonat is a amazing device , but on Mac is still have a clicking / noise sound when i try to play . I run Mac OSX 10.6.8 . Hope you can fix this version . Keep develope your great work . If you have any update please email me : Mg_halo@yahoo.com .Thanks you .

great read, mark. did you also experimented with pitchshifting /timestretching the ir´s?iam just about to patch something similar but with 2 ir´s that can be edited via the waveform~ object. great for fine adjustments…

regarding the chopper: there is a simple way to cut audio in max using ircam´s ftm library and catart. this patch will create the new audiofiles where you save it. here you go:

Hi Johannes, I'd be interested in seeing your IR pitch shifting technique if you want to share it. I have done something similar but only by copying between two buffers. Get in touch! Thanks for the CataRT tip... need to check that out again.

Hey Mark - it's wetterberg from the cycling74 forum, I'm wondering if I could somehow access the impact sounds that are in the application? I'm trying to get the ResonatorBpatch2 bpatch to work as a patch, but it's really difficult without the sounds - which are clearly included in the app.